Combination anti-icing additive for jet fuels



United States Patent search and Engineering (Zompany, a corporation ofDelaware No Drawing. Filed Mar. 15, 1961, Ser. No. 95,825 '7 Claims.(Cl. 44-63) The present invention concerns hydrocarbon oil compositions,particularly jet fuels, having improved water tolerance characteristicsand a process for operating jet engines utilizing said fuels. Moreparticularly, the instant invention relates to turbojet fuelcompositions having incorporated therein additives to reduce persistenthaze and stable emulsions formed when such fuels containing hazepromoting anti-icing additives are contacted by water.

The operating of jet engines at widely varying conditions of temperatureand altitude has resulted in grave problems in regard to suitable fuelcompositions to be utilized. One particularly serious problem involvesthe operational hazards of employing jet fuel containing dissolved andsuspended water at low temperatures and at high altitudes. Jet engineaircraft are normally equipped with filters located in the fuel pumpingsystem in order to remove suspended matter in fuel which might interferewith normal engine operation. At low temperatures and especially at thelow subfreezing temperatures, such as from --45 F. to 76 5., associatedwith high altitudes, dissolved and suspended water in the jet fuel formsice in the narrow passageways of the fuel flow system or on the filtersurface or on the sludge layer on the filter surface. Hydrocarbonsutilized as jet fuels are capable of dissolving small quantities ofWater from the air during normal weather, from storage tanks, and thelike. Additionally, water from these sources can also become suspendedin the fuel after it has become Water saturated. It is this dissolvedand suspended water which, upon lowering of the temperature, freezes andcreates an icing problem. The formation of ice results in the creationof a considerable pressure drop in the fuel system and sometimes thecomplete obstruction of the fuel how with resultant flameout and loss ofthe aircraft.

In order to alleviate this critical problem, anti-icing additives havebeen incorporated into jet fuel compositions to allow operation of theaircraft at low temperatures without excessive ice formation. Theseadditives have usually been aliphatic oxygen-containing compounds havingfrom about 1 to 30 carbon atoms per molecule. Typical anti-icingcompounds utilized in the past have included ether alcohols, such asalkoxy alkanols formed by the reaction of ethylene oxide or propyleneoxide with aliphatic alcohols, for example, ethanol and the like, toyield compounds such as Z-methoxyethanol, Z-ethoxyethanol and the like;alcohols, such as alkanols, for eX- ample, methanol, ethanol,isopropanol, and the like; glycols, such as alkanediols, like ethyleneglycol, propylene glycol, hexylene glycol, and the like; polyalkyleneglycols, such as polyethylene glycol and the like; alkanol amines, suchas aminomethyl propanol and the like; ethers, such as alkyl ethers, likeisopropanol ethers, and alkoxyl alkanol ethers, such as.bis(2-meth-oxyethyl)ethers; ether esters, such as alkoxy alkanol estersof 10W molecular Weight monocarboxylic acids, such as Z-methoxyethylacetate and the like. These additives and combinations thereof areparticularly useful as anti-icing additives ous problem.

and in general are set forth in US. Patents 2,952,121, 2,701,754,2,840,461, 2,722,099, 2,668,522, 2,599,338 and so forth.

Although these additives have generally helped to alleviate the icingeffects by function as freezing point depressants or surfactants theyhave created a new and seri- In general, these anti-icing additives allexhibit a pronounced tendency to suspend water with which thehydrocarbon fuel comes in contact and to yield stable oil-in-wateremulsions and persistent aqueous haze formations. Thus, these additives,particularly the aliphatic glycols of from 6 to 21 carbon atoms permolecule, and additive anti-icing combinations containing these glycolshave a particular tendency to promote aqueous haze conditions when jetfuel containing these additives contacts Water. The formation ofpersistent aqueous haze or stable water-in-oil emulsions in these fuelsmay adversely affect the performance of these fuels under.

severe operating conditions. Additionally, these stable emulsionsinduce'corrosion and in general affect the appearance, marketability,and consumer acceptance of the petroleum product. Since water exists inmost storage tanks, pipelines, and other container vessels during thehandling, transportation and storage of the fuel, haze formation andemulsions are also impossible to avoid.

It is, therefore, an object of this invention to reduce the tendency ofhydrocarbon oils containing haze-promoting anti-icing additives fromforming persistent haze or stable emulsions when contacted with water. Afurther object is to promote the marketability and appearnce of jetfuels by reducing the tendency of these fuels containing aliphaticoxygen anti-icing additives to form aqueous haze conditions. Further.objects and benefits are apparent to those skilled in the are in lightof the instant disclosures. I

The applicant has discovered that the incorporation into hydrocarbon oilcompositions of a minor amount of an alkyl pyrrolidone destabilizes andinhibits aqueous haze formation and Water-in-oil emulsions induced byhazepromoting anti-icing additives. It hasbeen found that thesealkylpyrrolidones are particularly effective in jet fuel compositionscontaining aliphatic oxygen-containinganti-icing additives of from 1 to30 carbon atoms. More particularly, the N-alkyl pyrrolidones have beenfound to be especially effective in reducing aqueous haze induced byaliphatic glycols. The pyrrolidones of this invention may beincorporated into the hydrocarbon oil either before or after thecontacting of water by the said oil. These pyrrolidones may be utilizedincornbination with the anti-icing additives in a concentrate form' Thepyrrolior added singly into the hydrocarbon oil. dones suitable for thepurposes of this invention include those alkyl substituted pyrrolidoneswherein the alkyl radical has from 1 to 4 carbon atoms. Preferred due totheir efficacy are N-alkyl pyrrolidones, while especially preferred byreason of commercial availability and performance' are the N-alkyl-Z-pyrrolidones, such as N- methyl-Z-pyrrolidone.

It should be noted that the employment of pynrolidone itself is notsuitable for the purposes of this invention due to its restrictive andlimited solubility in hydrocarbon oils. The applicant has found that hisinventive compounds exhibit a-suitable solubility balance such thateffective dehazing is accomplished. The quantity of the inventivepyrrolidones required to be utilized depends to some extent on theparticular anti-icing additive employed and its concentration level.Usually minor amounts ofpyrrol- Patented Dec. 29, 1964 J; idones areeffective, i.e. from about 0.01 to 2.0% by volume, with from 0.1 to 1.0%by volume normally effective. The ratio of anti-icing additive to thepyrrolidones ranges from 1/10 to 1, with from 1/4 to 2/ 1 particularlyeifective. The anti-icing additive are usually incorporated in minoramounts suflicient to give the effective anti-icing protection desired.These amounts commonly range from 0.001% by volume to about 3.0% byvolume, with from 0.05% to about 1.5% by volume the most common amountemployed.

Suitable pyrrolidones for the punposes of this invention include thefollowing: 3-methyl-N-methyl-2-pyrrolidone,4-ethyl-N-ethyl-2-pyrrolidone, N-ethyl-S-pyrrolidone, 3,4-dimethyl-N-methyl-Z-pyrrolidone, N-methyl-Z pyrrolidone, N-ropyl-2-pyrrolid0ne; and the like.

The commonly employed glycols include those akyl glycols having from 2to 21 carbon atoms per molecule, such a the mono, di, tri and higherglycols of ethylene, propylene, isobutylene, and the like, andespecially those alkyl diols characterized by having an alkyl radicaldirectly attached to at least one ofthe carbon atoms to which a hydroxylgroup is attached. The alkyl group may contain from 1 to 4 carbon atoms,although it is preferred that the alkyl group be a methyl group. Amongthe preferred diols, those having from 6 to 8 carbon atoms are mostpreferred, particularly the alkyl glycols as the hexylene glycols, as,for example, Z-methyl-Z,4-pentanediol, and hexanediol-2,5. Especiallypreferred among the hexylene glycols is Z-methyl-Z,4-pentanediol.

The hydnooarbon oils in which the additives of this invention may beincorporated are those hydrocarbon fuels boiling between about 250 F.and 750 F. and particularly those liquid petroleum turbojet fuelsboiling in the range between about 300 F. and 550 F. These fuels includethose used to power turboprop, turbofan, ramjet, pulsejet and similarjet engines. These fuels normally contain at least 10% by volume ofparafiinic components and meet ASTM Specification for Aviation TurbineFuels D-l 655-59T. These fuels are additionally defined by MilitarySpecifications MIL-L5 161E (ASG), MIL-J- 5'624E, MIL-F-25524A (USAF),and the like, and are generally referred to as JP-4, JP5, and JP-6. Theinventive additives may also be incorporated into heating oils, dieseloils, transformer oils, turbine oils, lubricating oils, and the likecontaining aliphatic oxygen-containing additives which promote theformation of a persistent aqueous haze condition when contacted withwater. Diesel fuels are as described in ASTM Specification D- 97553T,while heating oils are described in ASTM Specification D396-48T,particularly those in Grades 1 and 2 thereof. These fuels, in additionto the anti-icing and inventive additives, may include rust inhibitors,antistatic additives, corrosion inhibitors, dyes, dye stabilizers,polymeric additives, and the like.

The persistence of the haze formed in oil upon contact with water ismeasured in Waring Blendor Haze Tests wherein five milliliters of waterand 500 milliliters of the oil, such as IP4, with and without hazepromoting additives are mixed in a Waring Blender for a period of oneminute; the oil-water mixture is then observed over a specified timeperiod. The amount of light which is transmitted through the oil understandardized conditions is measured, or the haze and emulsificationconditions of the fuel are visibly observed during this time period.Where measured, the light transmission is expressed as a percentage ofthe total light emitted from the source.

These test methods have been found to be an extremely effective meansfor determining the degree to which haze is present in hydrocarbon oils.

The effectiveness of the present inventive combination may beascertained by the following examples.

EXAMPLE 1 The Waring Blendor test as described was conducted using 2.JP-4 jet fuel containing a well known commercial .13. anti icingadditive of hexylene glycol, i.e. 2-rnethyl-2,4-

entanediol. The results obtained are as indicated in bl I Table I 5DEHAZING JET FUEL (JP-4) CONTAINING AN ANTI-ICING ADDITIVE Percent LightTransmission 10 Additive Time in Hours Alter Mixing JP-4 Fuel 92 95 98.599.5 100 r J P4|0.20% hexylene gly- 1.) JPcpiq 6.2. fi. .t fi 1 2 85 8995 98 99 99.5 100 0 -me y pyrrolidoiie 90 93 97.5 99.5 100 J P4-|-0.2%hexylene glypyrrohdone 90 93 97.5 98.5 99.5 100 Jl-4+O.25% hexylene glyprolidone 99 99.5 100 JP4+0.2S% Additive X 82 S7 90 96 97 99.5 100IPA-{0.25% Additive X +0.25% LN -rnethyl-2-pyrrohdone 89 93 97 100 lN0teis a mixture of 67% hoxylene glycol+33% Z-methoryethanol.

The above results indicate the remarkable effectiveness with which thealkyl pyrrolidones eliminate stable haze conditions caused inhydrocarbon oil compositions by the presence of well knownhaze-promoting antiicing additives, such as hexylene glycol and mixturesof hexylene glycol with alkoxy alkanols. The anti-icing additivesemployed are those commonly accepted as effective anti-icing additivesfor incorporation in jet fuels for operating jet engines at subfreezingtemperatures.

The results acrieved by the alkyl pyrrolidones are rendered completelyunexpected in that the use of N-methyl- 2-pyrrolidone alone in JP-4slightly increased the the haze in the JP-4 over the fuel without anyadditive.

EXAMPLE 2 EXAMPLE 3 The water tolerance properties of a turbojet enginefuel boiling between about 275 F. and about 480 F. and containing 0.3%by volume of isopropanol and about 0.2% by volume of2-methyl-2,4-pentanediol is considerably improved by the addition ofabout 0.5% by volume of N-ethyl-2-pyrrolidone.

EXAMPLE 4 Aqueous haze clearance is promoted by the addition of about2.0% by volume of N-methyl-3-pyrrolidone to a heating oil boiling in therange between 324 F. and 645 F. and consisting of more than 10% byvolume of catalytically cracked stock and containing about 1.0% byvolume of isopropanol.

EXAMPLE 5 A turbojet fuel (JP-4) containing about 0.2% by volume ofZ-methoxy ethanol and forming a stable oilin-water emulsion whencontacted with water is eifec tively demulsified by the incorporation ofabout 0.1 volume percent of 3,3-dimethyl-N-methyl-Z-pyrrolidone.

From the foregoing examples, the remarkable eifectiveness of alkylpyrrolidones in reducing aqueous haze formation in hydrocarbon oils isdemonstrated. The results are particularly surprising wherein additivestending to stabilize oil-in-water emulsions are dehazed by the additionof N-methyl-Z-pyrrolidone. The effectiveness of the additives of thisinvention permits a significant improvement in -the marketability,appearance, and water tolerance properties of petroleum products andsimplifies the handling and the storage of such products.

What is claimed is:

1. A liquid hydrocarbon fuel boiling in the range of about 250 F. to 750F. containing an alkyl diol having 2 to 21 carbon atoms per moleculeadditive in suflicient quantity to provide anti-icing protection and insuflicient quantity to promote the formation of an aqueous haze whensaid fuel is contacted with water; said fuel also containing a minoramount suflicient to dehaze said fuel of an N-alkyl pyrrolidone.

2. A composition as claimed in claim 1 wherein said fuel is a turbojetengine fuel boiling in the range between 300 F. and 550 F.

3. A composition as claimed in claim 1 wherein said N-alkyl pyrrolidonehas from 1 to 4 carbon atoms in the alkyl radical.

4. A composition as claimed in claim 1 wherein said minor amount is aconcentration of from about 0.01% by volume to about 2.0% by volume.

5. A liquid hydrocarbon fuel boiling in the range between 300 F. and 550F. containing an alkyl diol having 2 to 21 carbon atoms per molecule insufiicient quantity to overcome icing effects and which is suflicient topromote the formation of an aqueous haze when said fuel is contactedwith Water and to which has been added from about 0.2% to 1.0% by volumeof a N-alkyl pyrrolidone wherein the alkyl radical has from 1 to 3carbon atoms.

6. A composition as defined by claim 5 wherein said alkyl diol is2-methyl-2,4-pentanediol.

7. A composition as claimed in claim 5 wherein said N-alkyl pyrrolidoneis N-methyl-Z-pyrrolidone and wherein said alkyl diol is hexyleneglycol.

' References Cited in the file of this patent UNITED STATES PATENTS2,550,981 Eberz May 1, 1951 2,550,982 Eberz May 1, 1951 2,701,754Haworth Feb. 8, 1955 2,722,099 Wasserbach Nov. 1, 1955 FOREIGN PATENTS1,020,209 Germany Nov. 28, 1957 9 OTHER REFERENCES German application1,094,037/ (Kl. 46a 7), Dec. 1, 1960.

1. A LIQUID HYDROCARBON FUEL BOILING IN THE RANGE OF ABOUT 250*F. TO750*F. CONTAINING AN ALKYL DIOL HAVING 2 TO 21 CARBON ATOMS PER MOLECULEADDITIVE IN SUFFICIENT QUANTITY TO PROVIDE ANTI-ICING PROTECTION AND INSUFFICIENT QUANTITY TO PROMOTE THE FORMATION OF AN AQUEOUS HAZE WHENSAID FUEL IS CONTACTED WITH WATER; SAID FUEL ALSO CONTAINING A MINORAMOUNT SUFFICIENT TO DEHAZE SAID FUEL OF AN N-ALKYL PYRROLIDONE.